1. Technical Field
The present invention relates in general to improved data detecting methods. In particular, the present invention relates to improve data detecting methods in the presence of intersymbol-interference (ISI) and noise. Still more particularly, the present invention relates to improved data detecting methods in the presence of intersymbol-interference (ISI) and noise in magnetic storage systems.
2. Description of the Related Art
In storage systems (such as DASD systems) as well as in data transmission systems, the signal read from the storage device or received at the output of a transmission channel has to be converted in the receiver into a sequence of symbols which most likely represents the data (symbol) sequence initially stored or transmitted, despite intersymbol-interference (ISI) between adjacent symbols, and despite added noise. The optimum receiver for detecting an uncoded data sequence in the presence of intersymbol-interference (ISI) and noise consists of a whitened-matched filter followed by a Viterbi detector that performs maximum likelihood sequence detection on the ISI trellis. In partial-response maximum likelihood systems (PRML) the composite noise at the input of the Viterbi detector is not white resulting in sub-optimal performance. This sub-optimality is more pronounced at high recording densities since the linear partial-response class 4 (PR4) equalizer tends to enhance the electronics. noise component of the composite noise at the input of the PRML detector. In addition to colored electronics noise, the media noise performance of a PRML system.
The International Patent Application with publication number WO97/11544, filed on Sep. 18, 1995, presently assigned to the assignee of the instance application, discloses a scheme for data detection in a direct access storage device, called noise-predictive maximum likelihood (NPML), that arises by imbedding a noise prediction/whitening filter into the branch metric computation of the Viterbi detector. It has been shown via simulations that ht NPML detectors offer substantial performance gains over the PRML detectors. The International Patent Application PCT/IB97/00554, filed on May 15, 1997, presently assigned to the assignee of the instant application, discloses a more efficient and simpler realization of the noise prediction/whitening mechanism in the NPML detector via infinite impulse response (IIR) predictors. The patent application with application Ser. No. 08/859,983, filed on May 21, 1997 and presently assigned to the assignee of the instant application, discloses a scheme where the noise prediction mechanism is implemented as a post-processor. In this patent application the noise whitening filter is implemented as an IIR filter optimized for disk noise only. This noise-prediction post-processor is based on the matched filter principle and corrects only the shortest minimum distance error at the output of the PRML detector. Another enhanced NPML detector scheme is disclosed in the U.S. patent application with application Ser. No. 09/144,230 which was filed Aug. 31, 1998 and which is presently assigned to the assignee of the instant application. The enhanced NPML detector scheme makes use of the xe2x80x9cone-shotxe2x80x9d receiver principle and corrects a preselected number of error events at the output of the PRML detector.
U.S. Pat. No. 5,521,945, currently assigned to Quantum Corporation, discloses an extended PR4 (EPR4) reduced complexity post-processor for PR4 Viterbi detectors. This post-processor uses the xe2x80x9cmerge-bitxe2x80x9d information produced by the PR4 Viterbi detector to identify and correct the most likely minimum distance error event on the 8-state EPR4 trellis. In the presence of electronics noise and at linear recording densities around PW50/T=2.7 this scheme performs about 0.2 dB worse than the eight-state EPRML detector and about 1.4 dB better than the PRML detector. In the presence of disk noise this performance benefit of the EPR4 post-processor starts to disappear.
From the foregoing it can be appreciated that it would be advantages to have an improved method of detecting data in the presence of intersymbol-interference (ISI) and noise.
It is therefore one object of the present invention to provide an improved method of data detection. It is another object of the present invention to provide an improved method data detection in the presence of intersymbol-interference (ISI) and noise. It is yet another object of the present invention to provide an improved method of detecting data in the presence of intersymbol-interference (ISI) and noise in magnetic storage systems.
It is still another object of the present invention to provide an improved method of detecting a data sequence received via any kind of partial-response data channel in the presence of intersymbol-interference (ISI) and noise.
The foregoing objects are achieved as in now described.
A method for use in connection with any kind of detector that receives an input signal via a partial-response channel and which provides a detector output signal and a merge-bit signal. According to the present scheme, the colored noise of the input signal is whitened in order to produce a filtered signal. The filtered signal is filtered to provide a first output signal using a second matched filter. The merge-bit signal is used to adjust the first matched filter to match a first most likely error event and to adjust the second matched filter to match a second most likely error event. It is then determined whether said first likely error event or said second likely error event is the most likely error event, and the actual errors of detector output signal are corrected using said most likely error event.
The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.